Bug 1313488 - Part 0: Adding missing includes. r=froydnj

Add missing includes to fix unified builds.

MozReview-Commit-ID: 3xkozGdrdBf

xpcom/tests/gtest/TestObserverService.cpp

@@ -11,6 +11,7 @@
 #include "nsComponentManagerUtils.h"
 
 #include "nsCOMPtr.h"
+#include "nsString.h"
 #include "nsWeakReference.h"
 
 #include "mozilla/RefPtr.h"